Convert the check-for-missing files check to a python script

'git ls-files --exclude=<pattern>' was changed (intentionally!)
not to exclude anything files that are actually in the index.
Since git ls-files by default simply lists the files in the
index, this is a problem. Emulating this in shell went past
the limits of what made sense, so move it to a simple external
python script.

tools/check-for-missing.py

@@ -0,0 +1,25 @@
+#!/usr/bin/python
+#
+# This is a simple script that we use to check for files in git
+# and not in the distribution. It was previously written in shell
+# and inlined in the Makefile.am, but 'git ls-files --exclude=<pattern>'
+# was changed to no longer due anything useful, which made that
+# too challenging to be worthwhile.
+
+import fnmatch, os, subprocess, sys
+
+srcdir=sys.argv[1]
+distdir=sys.argv[2]
+excludes=sys.argv[3:]
+
+os.chdir(srcdir)
+
+status=0
+for f in subprocess.Popen(["git", "ls-files"], stdout=subprocess.PIPE).stdout:
+    f = f.strip()
+    if (not os.path.exists(os.path.join(distdir, f)) and
+        not any((fnmatch.fnmatch(f, p) for p in excludes))):
+        print "File missing from distribution:", f
+        status=1
+
+sys.exit(status)